Semiconductor film and method of producing the same, photoelectric conversion element, solid-state imaging element and electronic apparatus

ABSTRACT

To provide a semiconductor film capable of realizing further enhancement of photoelectric conversion efficiency. The semiconductor film includes semiconductor nanoparticles and a compound represented by the following general formula (1), in which the compound represented by the general formula (1) is coordinated to the semiconductor nanoparticles.(In the general formula (1), X represents —SH, —COOH, —NH2, —PO(OH)2, or —SO2(OH), A1 represents —S, —COO, —PO(OH)O, or —SO2(O), and n is an integer of 1 to 3. B1 represents Li, Na, or K.)

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/317,371, filed 11 Jan. 2019, which is a national stage applicationunder 35 U.S.C. 371 and claims the benefit of PCT Application No.PCT/JP2017/020973 having an international filing date of 6 Jun. 2017,which designated the United States, which PCT application claimed thebenefit of Japanese Patent Application No. 2016-142825 filed 20 Jul.2016, the entire disclosures of each of which are incorporated herein byreference.

TECHNICAL FIELD

The present technology relates to a semiconductor film, a method ofproducing a semiconductor film, a photoelectric conversion element, asolid-state imaging element and an electronic apparatus.

BACKGROUND ART

In recent years, for realizing extra miniaturization and higher imagequality in regard of digital cameras and the like, research anddevelopment of color imaging devices in which red, blue and greenabsorption layers are stacked have been under way.

For example, there have been proposed a semiconductor film includingaggregates of metal atom-containing semiconductor quantum dots and aspecific ligand coordinated to the semiconductor quantum dots, and amethod of producing the semiconductor film by use of a ligand longer inmolecular chain length than the specific ligand (see PTL 1).

In addition, there have also been proposed, for example, quantum dotsobtained by a process in which a halogen and oleylamine are coordinatedto quantum dots, and, after film formation, ligand exchange fromoleylamine to mercaptopropionic acid (MPA) is conducted (see NPL 1).Further, a film formed by dispersing quantum dots, to whichmercaptopropionic acid (MPA) has been coordinated, in dimethyl sulfoxide(DMSO), followed by a dip coating method has been proposed (see NPL 2),and a film formed by coordinating an amide compound to quantum dots,followed by decomposing the amide compound with an acid has beenproposed (see NPL 3).

CITATION LIST Patent Literature

-   PTL 1: JP 2014-112623A

Non-Patent Literature

-   NPL 1: NATURE NANOTECHNOLOGY, 2012-   NPL 2: NATURE COMMUNICATIONS, 2015-   NPL 3: ACS Appl. Mater. Interfaces 2015, 7, 21995-22000

SUMMARY Technical Problem

However, according to the technologies proposed by PTL 1 and NPL 1 to 3,further enhancement of photoelectric conversion efficiency may not beachieved.

In view of the foregoing, the present technology has been made inconsideration of the above-mentioned circumstances. It is therefore amain object to provide a semiconductor film, a method of producing asemiconductor film, a photoelectric conversion element, a solid-stateelement and an electronic apparatus which make it possible to realizefurther enhancement of photoelectric conversion efficiency.

Solution to Problem

The present inventors has made extensive and intensive researches forachieving the above object and as a result, has surprisingly succeededin drastically enhancing the photoelectric conversion efficiency,thereby coming to complete the present technology.

More specifically, according to the present technology, first, there isprovided a semiconductor film including semiconductor nanoparticles anda compound represented by the following general formula (1), in whichthe compound represented by the general formula (1) is coordinated tothe semiconductor nanoparticles.

In the general formula (1), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n is aninteger of 1 to 3. B¹ represents Li, Na, or K.

In addition, according to the present technology, there is provided asemiconductor film obtained by coating a substrate with a dispersioncontaining semiconductor nanoparticles and a compound represented by thefollowing general formula (2), in which the compound represented by thegeneral formula (2) is coordinated to the semiconductor nanoparticles.

In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound.

The semiconductor nanoparticles included in the semiconductor filmaccording to the present technology may selectively absorb at leastlight in a visible region.

The semiconductor nanoparticles included in the semiconductor filmaccording to the present technology may selectively absorb at leastlight in an infrared region.

Further, according to the present technology, there is provided a methodof producing a semiconductor film, the method including coating asubstrate with a dispersion containing semiconductor nanoparticles and acompound represented by the following general formula (2), in which thecompound represented by the general formula (2) is coordinated to thesemiconductor nanoparticles.

In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound.

In the method of producing a semiconductor film according to the presenttechnology, the semiconductor nanoparticles may selectively absorb atleast light in a visible region.

In the method of producing a semiconductor film according to the presenttechnology, the semiconductor nanoparticles may selectively absorb atleast light in an infrared region.

According to the present technology, there is provided a photoelectricconversion element including a semiconductor film according to thepresent technology, and a first electrode and a second electrode whichare disposed to face each other, in which the semiconductor film isdisposed between the first electrode and the second electrode.

Besides, according to the present technology, there is provided asolid-state imaging element in which at least a photoelectric conversionelement according to the present technology and a semiconductorsubstrate are stacked for each of a plurality of pixels arranged in aone-dimensional manner or a two-dimensional manner.

Further, according to the present technology, there is provided anelectronic apparatus including a solid-state imaging element accordingto the present technology.

Advantageous Effect of Invention

In accordance with the present technology, image quality and reliabilitycan be enhanced. Note that the effect described here is not necessarilylimitative, and any of the effects described in the present technologymay be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is figures illustrating schematically an example of a method ofproducing a semiconductor film according to a third embodiment to whichthe present technology is applied.

FIG. 2 is a cross-sectional view illustrating a configuration example ofa solid-state imaging element according to a fifth embodiment to whichthe present technology is applied.

FIG. 3 is a cross-sectional view illustrating schematically aconfiguration example of a photoelectric conversion element produced inExample 3.

FIG. 4 is a cross-sectional view illustrating schematically aconfiguration example of a photoelectric conversion element produced inExample 4.

FIG. 5 is a figure illustrating use examples of the solid-state imagingelement according to a fifth embodiment to which the present technologyis applied.

DESCRIPTION OF EMBODIMENTS

Preferred modes for carrying out the present technology will bedescribed below. The embodiments described below are examples of typicalembodiments of the present technology, by which the scope of the presenttechnology is not to be construed narrowly.

Note that the description will be made in the following order.

-   -   1. Outline of Present Technology    -   2. First Embodiment (Example of Semiconductor Film)    -   2-1. Semiconductor film    -   2-2. Semiconductor nanoparticles    -   2-3. Compound represented by general formula (1)    -   3. Second Embodiment (Example of Semiconductor Film)    -   3-1. Semiconductor film    -   3-2. Dispersion    -   3-3. Compound represented by general formula (2)    -   4. Third Embodiment (Example of Method of Producing        Semiconductor Film)    -   4-1. Method of producing semiconductor film    -   4-2. Film formation (Coating)    -   4-3. Specific example of method of producing semiconductor film    -   5. Fourth Embodiment (Example of Photoelectric Conversion        Element)    -   5-1. Photoelectric conversion element    -   5-2. First electrode    -   5-3. Second electrode    -   5-4. Electron transport layer    -   5-5. Hole transport layer    -   5-6. Substrate for photoelectric conversion element    -   5-7. Method of producing photoelectric conversion element    -   6. Fifth Embodiment (Example of Solid-State Imaging Element)    -   6-1. Solid-state imaging element    -   6-2. Back illumination type solid-state imaging element    -   6-3. Front illumination type solid-state imaging element    -   7. Sixth Embodiment (Example of Electronic Apparatus)    -   8. Use Examples of Solid-State Imaging Element to Which Present        Technology Is Applied    -   9. Seventh Embodiment (Example of Light Emitting Device)

Outline of Present Technology

First, an outline of the present technology will be described.

In order to realize enhanced performance and diversified functions of acolor imaging device mounted on a digital camera or the like, a progressin the technology concerning a photoelectric conversion element or alight emitting device in which semiconductor nanoparticles are used isessential.

For example, in production of a semiconductor nanoparticle layerincluding semiconductor nanoparticles, there is a technology in which along-chain ligand is coordinated to semiconductor nanoparticles, tothereby disperse the semiconductor nanoparticles in an organic solvent,a substrate is coated with the resulting dispersion to form a film, andthereafter ligand exchange to a short-chain ligand is performed, tothereby reduce a distance between the semiconductor nanoparticles,thereby enhancing carrier mobility. A semiconductor film obtained bythis technology, however, is insufficient in surface coating, whichleads to surface defects, and, through an intermediate level arisingfrom the surface defects, electrons and holes generated by photoelectricconversion would be recombined, resulting in deactivation.

For the purpose of enhancing surface coverage for the semiconductornanoparticles, there is a method in which a halogen atom ispreliminarily coordinated to crystal sites where coordination of theshort-chain ligand is hardly accomplished, and the surface coverage isthereby enhanced. In addition, there are a method in which nanoparticlesto which 3-mercaptopropionic acid as a short-chain ligand ispreliminarily coordinated are dispersed in dimethyl sulfoxide (DMSO) anddip coating is conducted, and a method in which a functional grouphaving an amide group is coordinated and after film formation, theligand is hydrolyzed by an acid to convert the ligand into a short-chainligand.

These three methods, however, have a problem that a desirable highphotoelectric conversion efficiency cannot be obtained, since acoordination rate is low, or suitability for film formation is poor dueto bad volatility of the dispersant (dimethyl sulfoxide (DMSO)) anddifficulty in removing the dispersant, or dispersion stability is poordue to the hydrolysis by an acid. In addition, where semiconductor filmsobtained respectively by these three methods are applied to lightemitting devices, there may arise a problem that a high light emissionefficiency also cannot be obtained.

The present technology has been completed as a result of the presentinventors' extensive and intensive investigations of the above-mentionedproblems. The present technology relates to a semiconductor film, amethod of producing a semiconductor film, a photoelectric conversionelement, a solid-state imaging element, and an electronic apparatus. Inaddition, the present technology may be applied to a light emittingdevice. For improving the photoelectric conversion efficiency of aphotoelectric conversion element and the light emission efficiency of alight emitting device which have been problems, the present technologyrelates to a semiconductor film containing semiconductor nanoparticleshaving undergone ligand exchange to a short-chain ligand which is acompound represented by the general formula (1) described later througha process in which a film is formed using a dispersion of semiconductornanoparticles having a compound represented by the general formula (2)described later, followed by ion exchange. Besides, by providing aphotoelectric conversion element and a light emitting device includingthe semiconductor film, the present technology solves theabove-mentioned problems. Further, by providing a solid-state imagingelement which includes the photoelectric conversion element and whichhas a high photoelectric conversion efficiency and a display apparatuswhich includes the light emitting device and which has a high lightemission efficiency, the present technology also solves theabove-mentioned problems.

2. First Embodiment (Example of Semiconductor Film 2-1. SemiconductorFilm

A semiconductor film according to a first embodiment of the presenttechnology is a semiconductor film including semiconductor nanoparticlesand a compound represented by the following general formula (1), inwhich the compound represented by the general formula (1) is coordinatedto the semiconductor nanoparticles.

In the general formula (1), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n is aninteger of 1 to 3. B¹ represents Li, Na, or K.

The semiconductor film according to the first embodiment of the presenttechnology can reduce an intermediate level or levels arising fromsurface defects of semiconductor nanoparticles, and because ofcontaining the semiconductor nanoparticles having high carrier mobility,can restrain recombination of electrons and holes, and can reduce a darkcurrent.

2-2. Semiconductor Nanoparticles

The semiconductor nanoparticles contained in the semiconductor filmaccording to the first embodiment of the present technology may bearbitrary semiconductor nanoparticles, and include, for example, atleast one of TiO₂, ZnO, WO₃, NiO, MoO₃, CuO, Ga₂O₃, SrTiO₃, SnO₂,InSnOx, Nb₂O₃, MnO₂, V₂O₃, CrO, CuInSe₂, CuInS₂, AgInS₂, Si, PbS, PbSe,PbTe, CdS, CdSe, CdTe, Fe₂O₃, GaAs, GaP, InP, InAs, Ge, In₂S₃, Bi₂S₃,ZnSe, ZnTe, ZnS, and the like. A particle diameter of the semiconductornanoparticle is an arbitrary size and is preferably 2 to 20 nm. A shapeof the semiconductor nanoparticle may be a sphere, an ellipsoid, or atriangular prism or the like.

It is preferable that the semiconductor nanoparticles selectively absorbat least light in a visible region. Examples of the semiconductornanoparticles for red light include PbSe, CdTe, PbS, Si, PbTe, CdSe,CuInSe₂, CuInS₂, AgInS₂, MnO₂, V₂O₃, CrO, GaAs, Fe₂O₃, InP, InAs, Ge,Bi₂S₃, CuO, and the like. Examples of the semiconductor nanoparticlesfor green light include CdS, GaP, ZnTe, and the like. Examples of thesemiconductor nanoparticles for blue light include WO₃, ZnSe, In₂S₃, andthe like. In addition, the semiconductor nanoparticles for red light canbe shortened in wavelength at an absorption end by reducing the particlesize, and therefore, the semiconductor nanoparticles for red light whichare reduced in particle size can be used as semiconductor nanoparticlesfor green light and those for blue light.

In addition, it is preferable that the semiconductor nanoparticlesselectively absorb at least light in an infrared region.

The semiconductor nanoparticles may selectively absorb at least light inan ultraviolet region.

2-3. Compound Represented by General Formula (1)

The compound contained in the semiconductor film according to the firstembodiment of the present technology is represented by the followinggeneral formula (1). The compound represented by the following generalformula (1) may be selected from the viewpoint of small steric hindranceat the time of coordination to the semiconductor nanoparticles.

In the general formula (1), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n is aninteger of 1 to 3. It is preferable that n is 1. B¹ represents Li, Na,or K.

The compound represented by the general formula (1) is coordinated tothe semiconductor nanoparticles as a short ligand. Since an ionic radiusof B¹⁺ ion which is an alkali metal (Li, Na, or K) ion is smaller thanan ionic radius of B²⁺ ion which is a cation of an organic compound (forexample, an imidazolium compound, a pyridinium compound, a phosphoniumcompound, an ammonium compound, or a sulfonium compound), the compoundrepresented by the general formula (1) is a shorter ligand as comparedto the ligand including the cation (B²⁺) of the organic compound (thecompound represented by the general formula (2)). Note that all thecompound represented by the general formula (1) contained in thesemiconductor film may be coordinated to the semiconductornanoparticles, or part of the compound represented by the generalformula (1) contained in the semiconductor film may be coordinated tothe semiconductor nanoparticles.

The compound represented by the general formula (1) is a short ligandwhich is coordinated to the semiconductor nanoparticles asaforementioned, and by the coordination of the compound represented bythe general formula (1) to the semiconductor nanoparticles, aninter-particle distance between the semiconductor nanoparticles can beshortened, and carrier mobility can be enhanced. In addition, since thecompound represented by the general formula (1) is an alkali metal salt,a decomposition temperature of the ligand can be improved.

3. Second Embodiment (Example of Semiconductor Film) 3-1. SemiconductorFilm

A semiconductor film according to a second embodiment of the presenttechnology is obtained by coating a substrate with a dispersioncontaining semiconductor nanoparticles and a compound represented by thefollowing general formula (2), and the compound represented by thegeneral formula (2) is coordinated to the semiconductor nanoparticles.Note that the semiconductor nanoparticles contained in the semiconductorfilm according to the second embodiment of the present technology are asmentioned above, and therefore, description thereof is omitted here.

In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound.

The semiconductor film according to the second embodiment of the presenttechnology can reduce an intermediate level or levels arising fromsurface detects of the semiconductor nanoparticles, and because ofcontaining the semiconductor nanoparticles having high carrier mobility,can restrain recombination of electrons and holes, and can reduce a darkcurrent.

3-2. Dispersion

The dispersion used for obtaining the semiconductor film according tothe second embodiment of the present technology contains thesemiconductor nanoparticles and the compound represented by the generalformula (2). The dispersion can be obtained by dispersing thesemiconductor nanoparticles and the compound represented by the generalformula (2) in a solvent. The solvent may be a polar solvent, or a lowpolar solvent, or a nonpolar solvent, but preferably, it is a polarsolvent. When the semiconductor nanoparticles to which the compoundrepresented by the general formula (2) is coordinated are dispersed in apolar solvent, dispersibility is enhanced. The polar solvent may be anarbitrary one, and examples thereof include methanol, ethanol,1-propanol, 2-propanol, 1-butanol, dimethyl formamide, dimethylsulfoxide, N-methyl formamide, and the like.

The semiconductor nanoparticles are the same as the semiconductornanoparticles contained in the semiconductor film in the firstembodiment of the present technology, and therefore, description thereofis omitted here. The compound represented by the general formula (2)will be described below.

3-3. Compound Represented by General Formula (2)

The compound contained in the semiconductor film in the first embodimentof the present technology is represented by the following generalformula (2).

In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. It is preferable that n is 1. B² represents animidazolium compound, a pyridinium compound, a phosphonium compound, anammonium compound, or a sulfonium compound.

B² may be selected in consideration of solubility or dispersibility insolvents, dissociability (PKa, PKb, or the like) to B²⁺ (cation), andthe like. Examples of the cation (B²⁺) of the imidazolium compoundinclude 1-methylimidazolium cation, 1,3-dimethylimidazolium,1,2-dimethylimidazolium, and 1-butylimidazolium. Examples of the cation(B²⁺) of the pyridinium compound include 1-methylpyridinium, and1-ethylpyridinium. Examples of the cation (B²⁺) of the ammonium compoundinclude tetrabutylammonium ion. Examples of the cation (B²⁺) of thesulfonium compound include triethyl sulfonium.

It is considered that, when X in the compound represented by the generalformula (2) is coordinate-bonded to the semiconductor nanoparticles, B²⁺is located at a terminal end (a part substantially opposite, on amolecular structure basis, to a coordinate bond part) in the compoundrepresented by the general formula (2). Since B²⁺ is a cation of anorganic compound, the semiconductor nanoparticles to which the compoundrepresented by the general formula (2) is coordinated are easilydispersed in solvents, particularly in polar solvents, so thatdispersibility is enhanced, and at the same time, the coordination rateof the compound represented by the general formula (2) to thesemiconductor nanoparticles in a dispersed state can be enhanced, andsurface defects of the semiconductor nanoparticles can be reduced.

A film is formed by coating a substrate with the above-mentioneddispersion; while the distance between the particles is long and itobstructs conduction of carriers in this state, ion exchange from B²⁺ inthe compound represented by the general formula (2) to B¹⁺ in thecompound represented by the general formula (A) makes it possible toshorten the inter-particle distance between the semiconductornanoparticles, and to achieve a high carrier mobility.

Since the part ion-exchanged by the ion exchange is from B²⁺ which is aterminal end of a ligand to B¹⁺ which is a terminal end of a shortligand, a reduction of surface defects is small even when a change froma dispersion state to a film state is made. Since the ligand exchangefrom a long ligand to a short ligand in the film state involves exchangeof the whole ligands in the film state, a coordination rate is low, andreduction of surface defects is large, so that a surface state in aninitial state cannot be maintained. The exchange to the alkali metal ionwhich is B¹⁺ in the compound represented by the general formula (A) bythe ion exchange insolubilizes the film (inclusive of an already layeredfilm) with respect to the solvent of the dispersion, whereby suitabilityto film formation (layering) by the Layer-by-Layer (LBL) methoddescribed later can be enhanced.

In addition, change to the alkali metal such as Na by the ion exchangecan enhance thermal resistance. In a case where an ordinary method isused, when any of Hs in HS—CH₂CH₂—COOH is replaced by Na, solubility isso poor that change to the short ligand and Na salt cannot be achievedby a single operation, and a two-stage method of once performing ligandexchange to a mercaptopropionic acid (MPA) ligand and then performingion exchange is adopted. In other words, the ion exchange has anexcellent effect that the process can be simplified.

3-4. Substrate

The substrate to be coated with the above-mentioned dispersion is aconcept including an electrode, and it may be a monolayer structure inwhich the substrate itself is an electrode, or may be a layeredstructure in which an electrode is layered on a support substrate of aninorganic material, a resin, or the like. In addition, the substrate maybe a layered structure in which an electrode and an insulating film arelayered on a support substrate of an inorganic material, a resin, or thelike. A shape, a size, and a thickness of the substrate are notparticularly limited, and can be selected, as required, according to aviewpoint of suitability for producing, a viewpoint of purpose of use,etc.

4. Third Embodiment (Example of Method of Producing Semiconductor Film)4-1. Method of Producing Semiconductor Film

A method of producing a semiconductor film in a third embodiment of thepresent technology is a producing method including coating a substratewith a dispersion containing semiconductor nanoparticles and a compoundrepresented by the following general formula (2), in which the compoundrepresented by the general formula (2) is coordinated to thesemiconductor nanoparticles. Note that the semiconductor nanoparticlesand the compound represented by the general formula (2) which are usedin the method of manufacturing the semiconductor film in the thirdembodiment of the present technology are as mentioned above, anddescriptions thereof are omitted here.

In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. It is preferable that n is 1. B² represents animidazolium compound, a pyridinium compound, a phosphonium compound, anammonium compound, or a sulfonium compound.

4-2. Film Formation (Coating)

Examples of a film forming (coating) method for the semiconductor filminclude a wet coating method. Here, specific examples of the coatingmethod include a spin coating method; an immersion method; a castingmethod; various printing method such as a screen printing method, an inkjet printing method, an offset printing method, and a gravure printingmethod; a stamping method; a spraying method; and various coatingmethods such as an air doctor coater method, a blade coater method, arod coater method, a knife coater method, a squeeze coater method, areverse roll coater method, a transfer roll coater method, a gravurecoater method, a kiss coater method, a cast coater method, a spraycoater method, a slit orifice coater method, and a calendar coatermethod.

4-3. Specific Example of Method of Producing Semiconductor Film

An example of the method of producing the semiconductor film will bedescribed referring to FIG. 1 . The method of producing thesemiconductor film illustrated in FIG. 1 is a so-called Layer-by-Layer(LBL) method. As illustrated in FIG. 1 , a semiconductor film isproduced in the order of (a)→(b)→(c)→[(d)→(e)]→(f). Note that, asdescribed later, [(d)→(e)] may be repeated according to the filmthickness of the semiconductor film (the number of times of layering).

FIG. 1(a) is a diagram illustrating a dispersion 50 a prepared bydispersing semiconductor nanoparticles 51 to which a long ligand 52 suchas oleylamine and oleic acid has been coordinated, in a nonpolar or lowpolar solvent (for example, octane).

Subsequently, a solution prepared by dissolving a compound representedby the general formula (2) (for example, tetrabutylammonium3-mercaptopropionate) in a polar solvent (for example, methanol) isadded to the dispersion 50 a. As illustrated in FIG. 1(b), ligandexchange from a long ligand 52 to a ligand 53 which is the compoundrepresented by the general formula (2) (for example, tetrabutylammonium3-mercaptopropionate) occurs, whereby a dispersion 50 b in which thesemiconductor nanoparticles 51 to which the ligand 53 is coordinated isdispersed in the polar solvent (for example, methanol) is prepared. Inthe state of the dispersion, the coordination rate of the ligand 53 tothe semiconductor nanoparticles 51 can be enhanced.

Next, as illustrated in FIG. 1(c), an electrode (substrate) 54 (forexample, TiO₂) is coated with a layer of the dispersion 50 b by spincoating, to form on the electrode (substrate) 54 a film containing thesemiconductor nanoparticles 51 to which the ligand 53 as the compoundrepresented by the general formula (2) (for example, tetrabutylammonium3-mercaptopropionate) is coordinated.

Subsequently, the organic cation B²⁺ (for example, tetrabutylammoniumcation) in the compound represented by the general formula (2) ision-exchanged to an alkali metal ion (for example, Na⁺) by an ionexchange method. As illustrated in FIG. 1(d), a film containing thesemiconductor nanoparticles 51 to which a short ligand 55 as a compoundrepresented by the general formula (1) (for example, sodium3-mercaptopropionate) is coordinated is formed on the electrode(substrate) 54. actions and effects offered by the ion exchange are asmentioned above.

Next, by use of the dispersion 50 b, a second layer is formed by spincoating (FIG. 1(e)), and further, as illustrated in FIG. 1(d), ionexchange is performed again. Specifically, by repeating FIG. 1(d) FIG.1(e), layering is repeated, whereby a semiconductor film having adesired film thickness is produced (FIG. 1(f)).

5. Fourth Embodiment (Example of Photoelectric Conversion Element) 5-1.Photoelectric Conversion Element

A photoelectric conversion element in a fourth embodiment of the presenttechnology is a photoelectric conversion element including thesemiconductor film of the first embodiment or the semiconductor film ofthe second embodiment of the present technology, and a first electrodeand a second electrode which are disposed to face each other, in whichthe semiconductor film is disposed between the first electrode and thesecond electrode. In this case, the semiconductor film acts as aphotoelectric conversion film (photoelectric conversion layer). As willbe described later, an electron transport layer may be disposed betweenthe first electrode and the semiconductor film, and a hole transportlayer may be disposed between the second electrode and the semiconductorfilm. Note that the semiconductor film of the first embodiment or thesemiconductor film of the second embodiment that is provided in thephotoelectric conversion element of the fourth embodiment of the presenttechnology is as mentioned above, and therefore, description thereof isomitted here.

The photoelectric conversion element of the fourth embodiment of thepresent technology has the semiconductor film of the first embodiment orthe semiconductor film of the second embodiment, and therefore, anexcellent photoelectric conversion efficiency can be realized.

5-2. First Electrode

The first electrode provided in the photoelectric conversion element ofthe fourth embodiment of the present technology takes out a signalcharge (charge) generated in the semiconductor film. The first electrodeincludes, for example, a light-transmitting conductive material,specifically, ITO (Indium Tin Oxide). The first electrode may include,for example, a tin oxide (SnO₂) material or a zinc oxide (ZnO) material.The tin oxide material is a material obtained by adding a dopant to tinoxide. The zinc oxide material is, for example, aluminum zinc oxide(AZO) obtained by adding aluminum (Al) as a dopant to zinc oxide,gallium zinc oxide (GZO) obtained by adding gallium (Ga) as a dopant tozinc oxide, indium zinc oxide (IZO) obtained by adding indium (In) as adopant to zinc oxide, or the like. Other than these, it is also possibleto use IGZO, CuI, InSbO₄, ZnMgO, CuInO₂, MgIn₂O₄, CdO, ZnSnO₃, and thelike. A thickness (a thickness in a layering direction; hereinafterreferred to simply as thickness) of the first electrode may be anarbitrary thickness and is, for example, 50 to 500 nm.

5-3. Second Electrode

The second electrode provided in the photoelectric conversion element ofthe fourth embodiment of the present technology is for taking out holes.The second electrode may include a conductive material such as, forexample, gold (Au), silver (Ag), copper (Cu), and aluminum (Al). Likethe first electrode, the second electrode may include alight-transmitting conductive material. The thickness of the secondelectrode may be an arbitrary thickness and is, for example, 0.5 to 100nm.

5-4. Electron Transport Layer

The electron transport layer that may be provided in the photoelectricconversion element of the fourth embodiment of the present technologyaccelerates supply of electrons generated in the semiconductor film tothe first electrode and may include, for example, titanium oxide (TiO₂),zinc oxide (ZnO), or the like. Titanium oxide and zinc oxide may belayered on each other to compose the electron transport layer. Athickness of the electron transport layer may be an arbitrary thickness,and is, for example, 0.1 to 1,000 nm, preferably, 0.5 to 200 nm.

5-5. Hole Transport Layer

The hole transport layer that may be provided in the photoelectricconversion element of the fourth embodiment of the present technologyaccelerates supply of holes generated in the semiconductor film to thesecond electrode and may include, for example, molybdenum oxide (MoO₃),nickel oxide (NiO), vanadium oxide (V₂O₅), or the like. The holetransport layer may include an organic material such as PEDOT(Poly(3,4-ethylenedioxythiophene)), or TPD(N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine). A thickness of thehole transport layer may be an arbitrary thickness and is, for example,0.5 to 100 nm.

5-6. Substrate for Photoelectric Conversion Element

The photoelectric conversion element may be formed on a substrate. Here,examples of the substrate include organic polymers (having a form of apolymer material such as a plastic film or plastic sheet, or a plasticsubstrate including a polymer material and being flexible) exemplifiedby polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyvinylphenol (PVP), polyether sulfone (PES), polyimides, polycarbonate (PC),polyethylene terephthalate (PET), and polyethylene naphthalate (PEN).When the substrate including such a flexible polymer material is used,incorporation or uniting of an imaging element into or with anelectronic apparatus having, for example, a curved surface can beachieved. Alternatively, examples of the substrate include various glasssubstrates, various glass substrates formed with an insulating film on afront surface thereof, a quartz substrate, a quartz substrate formedwith an insulating film on a front surface thereof, a siliconsemiconductor substrate, and a metallic substrate of various alloys orvarious metals such as a stainless steel formed with an insulating filmon a front surface thereof. Note that examples of the insulating filminclude silicon oxide materials (for example, SiOx or spin-on-glass(SOG)); silicon nitride (SiN_(Y)); silicon oxynitride (SiON); aluminumoxide (Al₂O₃); metallic oxides and metallic salts. In addition, aninsulating film of an organic material can also be formed. Examples ofthe organic insulating film include polyphenol materials, polyvinylphenol materials, polyimide materials, polyamide materials,polyamide-imide materials, fluoropolymer materials, borazine-Si polymermaterials, and truxene materials, for which lithography can be used.Further, conductive substrates (substrates including a metal such asgold and aluminum, substrates including highly oriented graphite) formedwith an insulating film on a front surface thereof can also be used.

While the front surface of the substrate is desirably smooth, it mayhave such a degree of roughness as not to adversely affect thecharacteristics of the organic photoelectric conversion layer. Adhesionbetween the first electrode and the substrate or adhesion between thesecond electrode and the substrate may be enhanced by formation of asilanol derivative on the front surface of the substrate by a silanecoupling method, formation of a thin film including a thiol derivative,a carboxylic acid derivative, a phosphoric acid derivative, or the likeby a SAM method or the like, or formation of a thin film formed of aninsulating metallic salt or metal complex by a CVD method or the like.

5-7. Method of Producing Photoelectric Conversion Element

A method of producing the photoelectric conversion element of the fourthembodiment of the present technology will be described. Here, a casewhere the photoelectric conversion element of the fourth embodiment ofthe present technology has an electron transport layer and a holetransport layer will be described.

First, a first electrode is formed. Note that, in a case where thephotoelectric conversion element is formed on the substrate describedabove, the first electrode can be formed on the substrate for thephotoelectric conversion element. The first electrode is formed, forexample, by forming an ITO film by sputtering, and then performing dryetching or wet etching of the ITO film with patterning by aphotolithographic technique.

Next, an electron transport layer including, for example, titanium oxideis provided on the first electrode, followed by forming thesemiconductor film. The semiconductor film is formed by applying arelevant material to the electron transport layer by a wet film formingmethod, followed by a heat treatment. Examples of the wet film formingmethod include a spin coating method, an immersion method, a castingmethod, various printing method such as a screen printing method, an inkjet printing method, an offset printing method, and a gravure printingmethod, a stamping method, a spraying method, and various coatingmethods such as an air doctor coater method, a blade coater method, arod coater method, a knife coater method, a squeeze coater method, areverse roll coater method, a transfer roll coater method, a gravurecoater method, a kiss coater method, a cast coater method, a spraycoater method, a slit orifice coater method, and a calendar coatermethod. The heat treatment is performed in air, in a nitrogen (N₂)atmosphere or in an argon (Ar) atmosphere at, for example, 100° C. for30 minutes.

After the semiconductor film is provided, a film of, for example,molybdenum oxide or nickel oxide is formed to form the hole transportlayer. On the hole transport layer, a conductive film is formed by avacuum deposition method to form the second electrode, thereby producingthe photoelectric conversion element.

6. Fifth Embodiment (Example of Solid-State Imaging Element 6-1.Solid-State Imaging Element

A solid-state imaging element in a fifth embodiment of the presenttechnology is a solid-state imaging element in which at least thephotoelectric conversion element of the fourth embodiment of the presenttechnology and a semiconductor substrate are layered for each of aplurality of pixels arranged in a one-dimensional manner or atwo-dimensional manner. Examples of the solid-state imaging element ofthe fifth embodiment of the present technology include a backillumination type solid-state imaging element and a front illuminationtype solid-state imaging element. First, the back illumination typesolid-state imaging element will be described. Note that thephotoelectric conversion element of the fourth embodiment that isprovided in the solid-state imaging element of the fifth embodiment ofthe present technology is as mentioned above, and therefore, descriptionthereof is omitted here.

6-2. Back Illumination Type Solid-State Imaging Element

An example of the back illumination type solid-state imaging elementwill be described with reference to FIG. 2 . FIG. 2 is a cross-sectionalview illustrating a configuration example of one pixel 20 of a backillumination type solid-state imaging element 10.

The pixel 20 includes one photoelectric conversion element 41 as well asa photodiode 36 and a photodiode 37, both having a pn junction, whichare layered in a depth direction, in one pixel. The pixel 20 has asemiconductor substrate (silicon substrate) 35 in which the photodiode36 and the photodiode 37 are formed. A light receiving surface on whichlight is incident is formed on a back surface side of the semiconductorsubstrate 35 (an upper side of the semiconductor substrate 35 in FIG. 2), and a circuit including a reading circuit is formed on a frontsurface side of the semiconductor substrate 35. Thus, in the pixel 2,the light receiving surface on the back surface side of the substrate 35and the circuit formation surface formed on the substrate front surfaceside opposite to the light receiving surface are provided. Thesemiconductor substrate 35 may include a semiconductor substrate of afirst conductivity type, for example, n-type.

In the semiconductor substrate 35, two inorganic photoelectricconversion portions having a pn junction, namely, a first photodiode 36and a second photodiode 37 are formed in the manner of being layered ina depth direction from the back surface side. In the semiconductorsubstrate 35, the first photodiode 36 and the second photodiode 37 areformed in the depth direction (the downward direction in the figure)from the back surface side. In FIG. 2 , the first photodiode 36 is forblue color (B), and the second photodiode 37 is for red color (R).

On an upper portion of the back surface of the semiconductor substrate35 in a region where the first photodiode 36 and the second photodiode37 are formed, a photoelectric conversion element 41 for a first colorhaving a configuration in which a semiconductor film (photoelectricconversion layer) 32 has its upper and lower surfaces sandwiched by asecond electrode (upper electrode) 31 and a first electrode (lowerelectrode) 33 is layered. Note that, while not illustrated, thephotoelectric conversion element 41 may include an electron transportlayer and a hole transport layer. In the example of the backillumination type solid-state imaging element illustrated in FIG. 2 ,the photoelectric conversion element 41 is for green color (G). Thesecond electrode (upper electrode) 31 and the first electrode (lowerelectrode) 33 may include a transparent conductive film such as, forexample, an indium tin oxide film and an indium zinc oxide film.

As a combination of colors, in the example of the back illumination typesolid-state imaging element illustrated in FIG. 2 , the photoelectricconversion element 41 is for green color, the first photodiode 36 is forblue color, and the second photodiode 37 is for red color, but othercombination of colors can also be adopted. For example, thephotoelectric conversion element 41 may be set for red color or bluecolor, and the first photodiode 36 and the second photodiode 37 may beset for other corresponding colors. In this case, depth directionalpositions of the first photodiode 36 and the second photodiode 37 areset according to the colors.

In addition, three photoelectric conversion elements consisting of aphotoelectric conversion element 41B for blue color, a photoelectricconversion element 41G for green color, and a photoelectric conversionelement 41R for red color may be applied to the solid-state imagingelement (the back illumination type solid-state imaging element and thefront illumination type solid-state imaging element) of the fifthembodiment of the present technology, without using the first photodiode36 and the second photodiode 37. As the photoelectric conversion element41B for photoelectric conversion in regard of blue wavelength light,organic photoelectric conversion materials including coumarin dyes,tris(8-hydroxyquinoline)aluminum (Alq3), merocyanine dyes, and the likecan be used. As the photoelectric conversion element 41G forphotoelectric conversion in regard of green wavelength light, forexample, organic photoelectric conversion materials including rhodaminedyes, merocyanine dyes, quinacridone, and the like can be used. As thephotoelectric conversion element 41R for photoelectric conversion inregard of red wavelength light, organic photoelectric conversionmaterials including phthalocyanine dyes can be used.

Further, a photoelectric conversion element 41UV for ultraviolet lightand/or a photoelectric conversion element 41IR for infrared light may beapplied to the solid-state imaging element (the back illumination typesolid-state imaging element and the front illumination type solid-stateimaging element) of the fifth embodiment of the present technology, inaddition to the photoelectric conversion element 41B for blue color, thephotoelectric conversion element 41G for green color and thephotoelectric conversion element 41R for red color. With thephotoelectric conversion element 41UV for ultraviolet light and/or thephotoelectric conversion element 41IR for infrared light provided, it ispossible to detect lights of wavelengths other than the visible region.

In the photoelectric conversion element 41, the first electrode (lowerelectrode) 33 is formed, and an insulating film 34 for insulation of thefirst electrode (lower electrode) 33 is formed. Then, the semiconductorfilm (photoelectric conversion layer) 32 and the second electrode (upperelectrode) 31 thereon are formed on the first electrode (lowerelectrode) 33.

In one pixel 2, a wiring 39 connected to the first electrode (lowerelectrode) 33 and a wiring (not illustrated) connected to the secondelectrode (upper electrode) 31 are formed. The wiring 39 and the wiringconnected to the second electrode (upper electrode) 31 can be formedwith a tungsten (W) plug having an SiO₂ or SiN insulating layer in theperiphery thereof or a semiconductor layer by ion implantation, or thelike, for restraining short-circuiting with Si, for example. In theexample of the back illumination type solid-state imaging elementillustrated in FIG. 2 , the signal charge is electrons, and therefore,the wiring 39 is an n-type semiconductor layer, in the case of beingformed with a semiconductor layer by ion implantation. The secondelectrode (upper electrode) 31 is for drawing out holes, and therefore,a p-type can be used therefor.

In this example, an n-type region 38 for charge accumulation is formedon the front surface side of the semiconductor substrate 35. This n-typeregion 38 functions as a floating diffusion portion for thephotoelectric conversion element 41.

As the insulating film 34 on the back surface of the semiconductorsubstrate 35, a film having a negative fixed charge can be used. As thefilm having a negative fixed charge, a hafnium oxide film can be used,for example. In other words, the insulating film 34 may be formed in athree-layer structure in which a silicon oxide film, a hafnium oxidefilm and a silicon oxide film are sequentially formed from the backsurface side.

A wiring layer 45 is formed on the front surface side (the lower side inFIG. 2 ) of the semiconductor substrate 35; on the other hand, aprotective layer 44 is formed on the back surface side (the upper sidein FIG. 2 ) of the semiconductor substrate 35 and on the photoelectricconversion element 41, and a planarization layer 43 is formed on theprotective layer 44. An on-chip lens 42 is formed on the planarizationlayer 43. Though not illustrated, a color filter may be formed in theback illumination type solid-state imaging element 10.

6-3. Front Illumination Type Solid-State Imaging Element

The solid-state imaging element of the fifth embodiment of the presenttechnology is applicable not only to the back illumination typesolid-state imaging element but also to the front illumination typesolid-state imaging element. The front illumination type solid-stateimaging element will be described.

An example of the front illumination type solid-state imaging elementdiffers from the aforementioned back illumination type solid-stateimaging element 10 only in that a wiring layer 92 having been formed ata lower portion of the semiconductor substrate 35 is formed between thephotoelectric conversion element 41 and the semiconductor substrate 35.In other points, the front illumination type solid-state imaging elementmay be the similar to the aforementioned back illumination typesolid-state imaging element 10, and description thereof is omitted here.

7. Sixth Embodiment (Example of Electronic Apparatus)

An electronic apparatus in a sixth embodiment of the present technologyis an apparatus including the solid-state imaging element of the fifthembodiment of the present technology. The solid-state imaging element ofthe fifth embodiment of the present technology is as mentioned above,and therefore, description thereof is omitted here. The electronicapparatus of the sixth embodiment of the present technology includes thesolid-state imaging element having an excellent photoelectric conversionefficiency, and accordingly, enhancement of performance such as imagequality of color images can be realized.

8. Use Examples of Solid-State Imaging Element to which PresentTechnology is Applied

FIG. 5 is a figure illustrating use examples of the solid-state imagingelement of the fifth embodiment of the present technology as an imagesensor.

The aforementioned solid-state imaging element of the fifth embodimentcan be used in various cases, for example, a case of sensing light suchas visible light, infrared light, ultraviolet light, and X-rays asillustrated below. In other words, the solid-state imaging element ofthe fifth embodiment can be used for apparatuses (for example, theaforementioned electronic apparatus of the sixth embodiment) for use in,for example, a viewing field for imaging images for viewing use, atraffic field, a household appliance field, a medical or healthcarefield, a security field, a cosmetic field, a sports field, and anagricultural field.

Specifically, in the viewing field, the solid-state imaging element ofthe fifth embodiment can be used for apparatuses for imaging images forviewing use, such as, for example, digital cameras, smart phones, andmobile phones provided with a camera function.

In the traffic field, the solid-state imaging element of the fifthembodiment can be used for apparatuses for traffic use, such as, forexample, in-vehicle sensors for imaging the front side, the rear side,the surroundings, the interior, etc. of an automobile for the purpose ofsafe driving, such as automatic vehicle stop, recognition of thedriver's condition, etc., monitor cameras for monitoring the runningvehicles and/or the road, distance measuring sensors for measuringdistances such as inter-vehicle distance, etc.

In the household appliance field, the solid-state imaging element of thefifth embodiment can be used for apparatuses for use in householdappliances such as television receivers, refrigerators and airconditioners for the purpose of imaging a user's gesture and performingan apparatus operation according to the gesture, for example.

In the medical or healthcare field, the solid-state imaging element ofthe fifth embodiment can be used for apparatuses for medical orhealthcare use, such as endoscopes and devices for imaging blood vesselsby receiving infrared light, for example.

In the security field, the solid-state imaging element of the fifthembodiment can be used for apparatuses for security use, such assurveillance cameras for security and cameras for personauthentification, for example.

In the cosmetic field, the solid-state imaging element of the fifthembodiment can be used for apparatuses for cosmetic use, such as a skinmeasuring instrument for imaging a skin and a microscope for imaging thescalp, for example.

In the sports field, the solid-state imaging element of the fifthembodiment can be used for apparatuses for sports use, such as actioncameras and wearable cameras for sports uses or the like, for example.

In the agricultural field, the solid-state imaging element of the fifthembodiment can be used for apparatuses for agricultural use, such ascameras for monitoring conditions of fields and/or farm products, forexample.

9. Seventh Embodiment (Example of Light Emitting Device)

A light emitting device in a seventh embodiment of the presenttechnology includes two electrodes disposed to face each other and asemiconductor film disposed between the two electrodes. In this case,the semiconductor film acts as a light emitting film (light emittinglayer). The semiconductor film of the first embodiment and thesemiconductor film of the second embodiment of the present technologyare applicable as this semiconductor film. The semiconductor film of thefirst embodiment and the semiconductor film of the second embodiment ofthe present technology are as above-described. In the light emittingdevice of the seventh embodiment of the present technology, an electrontransport layer (n-type buffer layer) may further be disposed betweenthe semiconductor film and the electrode on one side, and a holetransport layer (p-type buffer layer) may further be disposed betweenthe semiconductor film and the electrode on the other side.

With the semiconductor nanoparticles contained in the semiconductor filmof the first embodiment and the semiconductor film of the secondembodiment of the present technology, the compound represented by theabove-mentioned general formula (1) is coordinated as a short ligand ata high coordination rate, and therefore, the surface level of thesemiconductor nanoparticles is lowered. It is considered that thesurface level of the semiconductor nanoparticles serves as a center ofnon-light-emitting recombination of electrons and holes present in thesame semiconductor nanoparticle. For this reason, when the semiconductorfilm of the first embodiment and the semiconductor film of the secondembodiment of the present technology are made to act as the lightemitting layer in the light emitting device of the seventh embodiment ofthe present technology, non-light-emitting recombination of electronsand holes injected into the light emitting layer from the electrontransport layer (n-type buffer layer) and the hole transport layer(p-type buffer layer) can be restrained. Therefore, according to thelight emitting device of the seventh embodiment of the presenttechnology, the proportion of light-emitting recombination is increased,and an effect of light emission at a higher luminance is produced.Besides, a display apparatus including the light emitting device of theseventh embodiment of the present technology can realize enhanceddisplay performance.

Note that embodiments of the present technology are not limited to theaforementioned embodiments, and various modifications are possiblewithout departing from the gist of the present technology.

In addition, the effects described in this specification are merelyexamples but not restrictive, and other effects may also be provided.

-   -   [1] A semiconductor film containing semiconductor nanoparticles        and a compound represented by the following general formula (1),    -   in which the compound represented by the general formula (1) is        coordinated to the semiconductor nanoparticles.

(In the general formula (1), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n is aninteger of 1 to 3. B¹ represents Li, Na, or K.)

-   -   [2] in which the compound represented by the general formula (2)        is coordinated to the semiconductor nanoparticles.

(In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound.)

-   -   [3] The semiconductor film as described in [1] or [2], in which        the semiconductor nanoparticles selectively absorb at least        light in a visible region.    -   [4] The semiconductor film as described in any one of [1] to        [3], in which the semiconductor nanoparticles selectively absorb        at least light in an infrared region.    -   [5] A method of producing a semiconductor film, the method        including coating a substrate with a dispersion containing        semiconductor nanoparticles and a compound represented by the        following general formula (2),    -   in which the compound represented by the general formula (2) is        coordinated to the semiconductor nanoparticles.

(In the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3. B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound.)

-   -   [6] The method of producing the semiconductor film as described        in [5], in which the semiconductor nanoparticles selectively        absorb at least light in a visible region.    -   [7] The method of producing the semiconductor film as described        in [5] or [6], in which the semiconductor nanoparticles        selectively absorb at least light in an infrared region.    -   [8] A photoelectric conversion element including a semiconductor        film as described in any one of [1] to [4], and a first        electrode and a second electrode which are disposed to face each        other,    -   in which the semiconductor film is disposed between the first        electrode and the second electrode.    -   [9] A solid-state imaging element in which at least a        photoelectric conversion element as described in [8] and a        semiconductor substrate are stacked,    -   for each of a plurality of pixels arranged on a one-dimensional        manner or a two-dimensional manner.    -   [10] An electronic apparatus including a solid-state imaging        element as described in [9].

EXAMPLES

The effects of the present technology will be described in detail belowby providing Examples. Note that the scope of the present technology isnot to be limited to or by Examples.

Example 1: Preparation of Dispersion 1

Example 1 is an example relating to preparation of Dispersion 1 for usein producing a semiconductor film containing semiconductornanoparticles, in a photoelectric conversion element using thesemiconductor nanoparticles. Specifically, Example 1 is an example inwhich Dispersion 1 is prepared by using PbS as semiconductornanoparticles and using tetrabuthylammonium 3-mercaptopropionate as aligand.

First, 0.1 g of spherical PbS with a diameter of 3 nm as semiconductornanoparticles to which oleic acid was coordinated was mixed with 5 ml ofoctane as a solvent, then a methanol solution of 0.1 g oftetrabutylammonium 3-mercaptopropionate was added to the solventcontaining the semiconductor nanoparticles, and the resultant mixturewas stirred by use of a stirrer at 500 rpm for 12 hours. In theabove-mentioned manner, Dispersion 1 of PbS to which tetrabutylammonium3-mercaptopropionate was coordinated and which was dispersed in methanolwas prepared. When Dispersion 1 thus prepared was left to stand at roomtemperature for one day, precipitation of the semiconductornanoparticles was not observed, and high dispersion stability wasconfirmed.

Example 2: Preparation of Dispersion 2

Example 2 is an example relating to preparation of Dispersion 2 for usein producing a semiconductor film containing semiconductornanoparticles, in a photoelectric conversion element using thesemiconductor nanoparticles. Specifically, Example 2 is an example inwhich Dispersion 2 was prepared by using PbS as semiconductornanoparticles and using hexyltrimethylammonium 3-mercaptopropionate as aligand.

First, 0.1 g of spherical PbS with a diameter of 3 nm as semiconductornanoparticles to which oleic acid was coordinated was mixed with 5 ml ofoctane as a solvent, then a methanol solution of 0.1 g ofhexyltrimethylammonium 3-mercaptopropionate was added to the solventcontaining the semiconductor nanoparticles, and the resultant mixturewas stirred by use of a stirrer at 500 rpm for 12 hours. In theabove-mentioned manner, Dispersion 2 of PbS to whichhexyltrimethylammonium 3-mercaptopropionate was coordinated and whichwas dispersed in methanol was prepared. When Dispersion 2 thus preparedwas left to stand at room temperature for one day, precipitation of thesemiconductor nanoparticles was not observed, and high dispersionstability was confirmed.

Example 3: Fabrication of Photoelectric Conversion Element 1

Example 3 is an example relating to fabrication of PhotoelectricConversion Element 1 by use of Dispersion 1 used for producing thesemiconductor film containing the semiconductor nanoparticles, in aphotoelectric conversion element using the semiconductor nanoparticles.Specifically, Example 3 is an example in which Photoelectric ConversionElement 1 was fabricated by using PbS as nanoparticles contained inDispersion 1 and using tetrabutylammonium 3-mercaptopropionate as aligand contained in Dispersion 1.

FIG. 3 shows Photoelectric Conversion Element 1 which includes asemiconductor film 103 and which was fabricated in Example 3. Infabricating Photoelectric Conversion Element 1, a first electrode 101including indium-doped tin oxide was formed in a thickness of 100 nm ona support substrate 100 including a quartz substrate, and an electrontransport layer 102 including titanium oxide was formed in a thicknessof 20 nm on the first electrode 101. Next, Dispersion 1 in which Pbswith a diameter of 3 nm to which tetrabutylammonium 3-mercaptopropionatewas coordinated was dispersed in methanol was applied to the firstelectrode 101 by spin coating. Subsequently, ion exchange was conductedby dropping an aqueous sodium hydroxide solution to the layer of PbSwith a diameter of 3 nm to which tetrabutylammonium 3-mercaptopropionatewas coordinated, the layer being formed by spin coating, after whichwashing with methanol was performed for removing tetrabutylammoniumhydroxide produced by the ion exchange. This film forming step wasrepeated to form the semiconductor film 103 in a thickness of 200 nm.Finally, a hole transport layer 104 including NiO was formed in athickness of 20 nm, and finally, a second electrode 105 includingindium-doped tin was formed in a film thickness of 100 nm, to completePhotoelectric Conversion Element 1 containing the semiconductornanoparticles.

Example 4: Fabrication of Photoelectric Conversion Element 2

Example 4 is an example relating to fabrication of PhotoelectricConversion Element 2 by use of Dispersion 2 used for producing thesemiconductor film containing the semiconductor nanoparticles, in aphotoelectric conversion element using the semiconductor nanoparticles.Specifically, Example 4 is an example in which Photoelectric ConversionElement 2 was fabricated by using PbS as nanoparticles contained inDispersion 2 and using hexyltrimethylammonium 3-mercaptopropionate as aligand contained in Dispersion 2.

FIG. 4 shows Photoelectric Conversion Element 2 which includes asemiconductor film 203 and which was fabricated in Example 4. Infabricating Photoelectric Conversion Element 2, a first electrode 201including indium-doped tin oxide was formed in a thickness of 100 nm ona support substrate 200 including a quartz substrate, after which anelectron transport layer 202 including titanium oxide was formed in athickness of 20 nm on the first electrode 201. Next, Dispersion 2 inwhich PbS with a diameter of 3 nm to which hexatrimethylammonium3-mercaptopropionate was coordinated was dispersed in methanol wasapplied to the first electrode 201 by spin coating. Dispersion 2 wasapplied to the first electrode 201 by spin coating. Subsequently, ionexchange was conducted by dropping an aqueous sodium hydroxide solutionto the layer of PbS with a diameter of 3 nm to whichhexyltrimethylammonium 3-mercaptopropionate was coordinated, the layerbeing formed by spin coating, after which washing with methanol wasperformed for removing hexyltrimethylammnoium hydroxide produced by theion exchange. This film forming step was repeated, to form thesemiconductor film 203 in a thickness of 200 nm. Finally, a holetransport layer 204 including NiO was formed in a thickness of 20 nm,and finally, a second electrode 205 including indium-doped tin wasformed in a film thickness of 100 nm, to complete PhotoelectricConversion Element 2 containing the semiconductor nanoparticles.

Comparative Example 1: Preparation of Metal Halide Precursor

Cadmium chloride (Sigma-Aldrich, 99.98%) or lead chloride (Alfa Aesar,99.999%) and TDPA (tetradecylphosphoric acid, Alfa Aesar, 98%) weredissolved in oleylamine (Acros, 80%) at 100° C. with deaeration for 16hours. A product thus obtained was stored at 80° C. in such a manner asto prevent solidification. As a typical procedure, 0.30 g (1.64 mmol) ofcadmium chloride and 0.033 g (0.12 mmol) of TDPA were dissolved in 5 mlof oleylamine, to prepare a precursor having a cadmium/TDPA molar ratioof 13.6:1.

Synthesis of Semiconductor Nanoparticles and Treatment of Metal Halide

Synthesis of lead sulfide nanoparticles (quantum dots) was conducted onthe basis of a known method. In performing a treatment of a metalhalide, 1.0 ml of the metal halide precursor was added to the sulfursource poured into a reaction vessel, followed by cooling slowly. Inthis synthesis, the lead/cadmium molar ratio was kept at 6:1. When thetemperature of the reaction system reached 30° C. to 35° C., 60 mL ofacetone was added, and centrifugation was conducted, to separatenanocrystals. The nanocrystals were dispersed in toluene, andreprecipitation was conducted using an acetone/methanol solution havinga volume ratio of 1:1, after which the precipitate was dissolved inanhydrous toluene. Further, a product thus obtained was washed two orthree times with methanol, and was dispersed in octane (50 mgmL⁻¹).

Fabrication of Photoelectric Conversion Element A

A lead sulfide nanoparticle (colloid quantum dot) (CQD) film formed bystacking layers through conducting spin coating for each layer in a roomtemperature atmosphere. For each layer, a CQD solution (50 mgmL⁻¹ octanesolution) was placed on a zinc oxide/titanium oxide substrate, and spincasting was conducted at 2,500 rpm. In a hybrid and organic technique,the layer surface was immersed in a methanol solution (1% v/v) of3-marcaptopropionic acid (MPA) for three seconds, and spin coating wasperformed at 2,500 rpm to effect ligand exchange in a solid state. Thisoperation was repeated until a desired film thickness was reached, toform a semiconductor film A in a thickness of 200 nm. Note that washingwith methanol was conducted twice, for removing the ligand loosened fromlinkage. Using this semiconductor film A, Photoelectric ConversionElement A was fabricated. The method of fabricating PhotoelectricConversion Element A was similar to that of Photoelectric ConversionElements 1 and 2 in Examples 3 and 4; a quartz substrate, a firstelectrode, an electron transport layer, the semiconductor film A, a holetransport layer, and a second electrode were stacked sequentially, tocomplete Photoelectric Conversion Element A.

Evaluation of Photoelectric Conversion Efficiency Method of MeasuringPhotoelectric Conversion Efficiency

Photoelectric conversion efficiency (external quantum efficiency:photon-electron conversion efficiency) of Photoelectric ConversionElement 1 (Example 3), Photoelectric Conversion Element 2 (Example 4)and Photoelectric Conversion Element A (Comparative Example 1) wasmeasured by use of light obtained by narrowing simulated solar lightsource (AM 1.5, 100 mW/cm²) to monochromatic.

Measurement Results of Photoelectric Conversion Efficiency

While the photoelectric conversion efficiency of PhotoelectricConversion Element A (Comparative Example 1) was 40%, PhotoelectricConversion Element 1 (Example 3) and Photoelectric Conversion Element 2(Example 4) each gave high photoelectric conversion efficiency of 60%.It could be verified that photoelectric conversion efficiency isenhanced by use of Photoelectric Conversion Element (Example 3) andPhotoelectric Conversion Element 2 (Example 4).

REFERENCE SIGNS LIST

-   -   1, 2 . . . Photoelectric conversion element,    -   10 . . . Back illumination type solid-state imaging element,    -   51 . . . Semiconductor nanoparticles,    -   55 . . . Short ligand,    -   100, 200 . . . Quartz substrate,    -   101, 201 . . . First electrode,    -   102, 202 . . . Electron transport layer,    -   103, 203 . . . Semiconductor film,    -   104, 204 . . . Hole transport layer,    -   105, 205 . . . Second electrode

What is claims is:
 1. A semiconductor film obtained by coating asubstrate with a dispersion containing semiconductor nanoparticles and acompound represented by general formula (2):

(in the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3, B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound), wherein the compound represented by the generalformula (2) is coordinated to the semiconductor nanoparticles.
 2. Thesemiconductor film according to claim 1, wherein the semiconductornanoparticles selectively absorb at least light in a visible region. 3.The semiconductor film according to claim 1, wherein the semiconductornanoparticles selectively absorb at least light in an infrared region.4. The semiconductor film according to claim 1, wherein thesemiconductor nanoparticles include at least one of TiO₂, ZnO, WO₃, NiO,MoO₃, CuO, GazO₃, SrTiO₃, SnO₂, InSnOx, Nb₂O₃, MnO₂, V₂O₃, CrO, CuInSe₂,CuInS₂, AgInS₂, Si, PbS, PbSe, PbTe, CdS, CdSe, CdTe, Fe₂O₃, GaAs, GaP,InP, InAs, Ge, In₂S₃, Bi₂S₃, ZnSe, ZnTe, or ZnS.
 5. The semiconductorfilm according to claim 1, wherein a particle diameter of thesemiconductor nanoparticle is 2 to 20 nm.
 6. The semiconductor filmaccording to claim 1, wherein a shape of the semiconductor nanoparticleis a sphere, an ellipsoid, or a triangular prism.
 7. The semiconductorfilm according to claim 1, wherein the semiconductor nanoparticles forred light include PbSe, CdTe, PbS, Si, PbTe, CdSe, CuInSe₂, CuInS₂,AgInS₂, MnO₂, V₂O₃, CrO, GaAs, Fe₂O₃, InP, InAs, Ge, Bi₂S₃ or CuO. 8.The semiconductor film according to claim 1, wherein the semiconductornanoparticles for green light include CdS, GaP or ZnTe.
 9. Thesemiconductor film according to claim 1, wherein the semiconductornanoparticles for blue light include WO₃, ZnSe or In₂S₃.
 10. Aphotoelectric conversion element, comprising: semiconductor filmobtained by coating a substrate with a dispersion containingsemiconductor nanoparticles and a compound represented by generalformula (2):

(in the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to 3, B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound), wherein the compound represented by the generalformula (2) is coordinated to the semiconductor nanoparticles; a firstelectrode; and a second electrode which are disposed to face each other,wherein the semiconductor film is disposed between the first electrodeand the second electrode.
 11. The photoelectric conversion elementaccording to claim 10, wherein the first electrode includes alight-transmitting conductive material such as ITO and the secondelectrode includes a conductive material such as Au, Ag, Cu or Al. 12.The photoelectric conversion element according to claim 10, wherein thesemiconductor nanoparticles selectively absorb at least light in avisible region.
 13. The photoelectric conversion element according toclaim 10, wherein the semiconductor nanoparticles selectively absorb atleast light in an infrared region.
 4. The photoelectric conversionelement according to claim 10, wherein the semiconductor nanoparticlesinclude at least one of TiO₂, ZnO, WO₃, NiO, MoO₃, CuO, GazO₃, SrTiO₃,SnO₂, InSnOx, Nb₂O₃, MnO₂, V₂O₃, CrO, CuInSe₂, CuInS₂, AgInS₂, Si, PbS,PbSe, PbTe, CdS, CdSe, CdTe, Fe₂O₃, GaAs, GaP, InP, InAs, Ge, In₂S₃,Bi₂S₃, ZnSe, ZnTe, or ZnS.
 15. The photoelectric conversion elementaccording to claim 10, wherein a particle diameter of the semiconductornanoparticle is 2 to 20 nm.
 16. The photoelectric conversion elementaccording to claim 10, wherein a shape of the semiconductor nanoparticleis a sphere, an ellipsoid, or a triangular prism.
 17. The photoelectricconversion element according to claim 10, wherein the semiconductornanoparticles for red light include PbSe, CdTe, PbS, Si, PbTe, CdSe,CuInSe₂, CuInS₂, AgInS₂, MnO₂, V₂O₃, CrO, GaAs, Fe₂O₃, InP, InAs, Ge,Bi₂S₃ or CuO.
 18. The photoelectric conversion element according toclaim 10, wherein the semiconductor nanoparticles for green lightinclude CdS, GaP or ZnTe.
 19. The photoelectric conversion elementaccording to claim 10, wherein the semiconductor nanoparticles for bluelight include WO₃, ZnSe or In₂S₃.
 20. A method of producing asemiconductor film, the method comprising: coating a substrate with adispersion containing semiconductor nanoparticles and a compoundrepresented by the following general formula (2):

(in the general formula (2), X represents —SH, —COOH, —NH₂, —PO(OH)₂, or—SO₂(OH), A¹ represents —S, —COO, —PO(OH)O, or —SO₂(O), and n representsan integer of 1 to
 3. B² represents an imidazolium compound, apyridinium compound, a phosphonium compound, an ammonium compound, or asulfonium compound), wherein the compound represented by the generalformula (2) is coordinated to the semiconductor nanoparticles.